5. Rotation of Maize with some Leguminous Food Crops for Sustainable Production on the Vertisols of the Accra Plains of Ghana

Abstract

Five food legumes were grown, as cover/food crops, in rotation with maize, at the University of Ghana, Soil and Irrigation Research Centre, Kpong. The legumes were determinate cowpea (Vigna unguiculata (L.) Walper, var. soronko), indeterminate cowpea (Vigna unguiculata (L.) Walper, var. Adidome mottled), soyabean (Glycine max (L.) Merril, var. GMX 92–16-2M), bambara groundnut (Vigna subterranea (L.) Verd, var. Ada) and groundnut (Arachis hypogea L., var. goronga). The experimental treatments were: incorporated legume residues, recommended inorganic fertilizer application (100 kg N, 60 kg P O and 40 kg K SO ha^-1) and no fertilization as 2 5 2 4 control. Soil samples (0-20 cm depth) were analysed for pH, organic carbon (OC) and nitrogen (N) contents before and after the experiments. Samples of the leguminous crops were also analysed for N content. The indeterminate cowpea continued growth after initial setting of pods and, therefore, had greater biomass (total dry weight – TDW) than the other leguminous crops. Its total N was relatively high in spite of lower N content. The TDWs of indeterminate cowpea, soyabean and groundnut were 2.80, 1.90 and 1.85 t ha^-1, respectively; the N contents were 2.7, 4.5 and 4.8% and the total N contents were 75.6, 91.2 and 83.3 kg ha^-1. Grain yields of maize were higher in the incorporated soyabean and groundnut treatments than the other leguminous crops. In the major rainy season in 2003, grain yield in the groundnut treatment was 3.3 t ha^-1, compared with 3.1 and 1.1 t ha-1 in the inorganic fertilizer treatment and the control, respectively. In the minor rainy season in 2004, grain yield was 3.0 t ha-1 in the soyabean treatment, compared with 3.0 and 1.6 t ha^-1 in the inorganic fertilizer and control treatments.